After a liquid processing of a substrate such as substrate cleaning, the substrate needs to be dried by removing the liquid on the surface of the substrate. For example, an attempt to remove the liquid on the substrate by vaporization may cause fine structures formed on the substrate to collapse by liquid surface tension. A drying method utilizing a sublimating material is being proposed to prevent the collapse of such structures.
The method of drying the substrate using a sublimating material begins with supplying a liquid containing a sublimating material to the surface of the substrate. The supplied liquid substitutes the cleaning liquid remaining on the substrate surface which was used in the cleaning of the substrate surface. Then, the liquid containing the sublimating material is vaporized to cause the sublimating material to precipitate in the spaces between the structures. As a result, the spaces between the structures are filled with solids of the sublimating material. Then the precipitate of the sublimating material is removed by sublimation to dry the substrate surface. In the above described method, it is possible to prevent the collapse of the structures caused by liquid surface tension since the structures are supported by solids of sublimating materials filled between the spaces of the structures.
Conventionally, the process of removing the sublimating material by sublimation was controlled, for example, by time. Thus, the determination of whether or not the sublimating material has sublimated sufficiently from the substrate surface was made, for example, by the eyes of the operator or by using SEM (Scanning Electron Microscope). Thus, it was difficult to properly detect the progress or the end point, i.e. end period of the process for removing the sublimating material by sublimation and end the process by such proper detection.